The present invention relates to the video processing system art. It finds particular application in conjunction with a wavelet domain filtering technique, and more particularly a method and apparatus for removing a checkerboard-like noise artifact from a captured composite NTSC video frame. However, it should be appreciated that the present invention may also find application in conjunction with other types of video processing systems and applications that input composite NTSC video signals.
The NTSC video standard is used by the United States and Japan. This standard specifies a signal transmission at 525 lines/frame at 30 frames/second with a 2:1 interlace. The composite NTSC video signal can be represented as:
l(x,y,t)=Y(x,y,t)+I(x,y,t) cos(2xcfx80fsx+"PHgr") cos[xcfx80(frtxe2x88x92fly)]Q(x,y,t) sin(2xcfx80fsx+"PHgr") cos[xcfx80(frtxe2x88x92fly)],xe2x80x83xe2x80x83Eq.1
where Y and (I, Q) are the luminance and the chrominance components, respectively; fs is the color subcarrier frequency; and fl an fr are the scan line and the frame frequencies, respectively.
Capturing still or freeze-frame pictures from a composite NTSC video signal for viewing on a progressive monitor, printing on a printer, inserting into an electronic document, etc. is a challenging problem in the area of video processing. Artifacts that may go unnoticed when looking at a moving video signal become extremely objectionable when viewing as a still picture.
In particular, when a composite NTSC video signal is captured, such as with a SUN Parallax video capture board, a checkerboard-like noise artifact can be observed on the vertical and diagonal edges in the captured video frame. The checkerboard-like artifact occurs in each of the interlaced fields (F1, F2) of the captured video frame. It is suggested that the checkerboard-like noise artifact may be a result of the quadrature demodulation and the corresponding chrominance shifts due to phase detection errors combined with the aliasing caused by the sampling of the color components during the process of A/D conversion.
Accordingly, it has been considered desirable to develop a new and improved method and apparatus for removing checkerboard-like noise artifact from a captured composite NTSC video frame that meets the above-stated needs and overcomes the foregoing difficulties and others while providing better and more advantageous results.
The present invention is directed to a wavelet domain filtering technique that removes or at least minimizes the checkerboard noise from a captured composite NTSC video frame. In the described embodiment, a Haar basis filter bank is used to obtain a wavelet decomposition. Low-pass filtering is performed on the high-high (HH) and the high-low (HL) bands since the checkerboard-like noise artifact is primarily visible on the vertical and the diagonal edges of the captured composite NTSC video frame.
In accordance with one aspect of the present invention, a method of processing a video frame captured from a moving video signal is disclosed. The method includes the steps of transforming the video frame into the wavelet domain to form a transformed video frame, filtering out noise artifacts present in the transformed video frame, and reconstructing the video frame from the transformed video frame to form a filtered video frame.
In accordance with another aspect of the present invention, an image processing apparatus is disclosed. The apparatus includes a frame grabber that generates a video-frame from a moving video signal, a first processor that transforms the video frame into the wavelet domain to form a decomposed video frame, a filter that removes noise artifacts present in the decomposed video frame, and a second processor that reconstructs the video frame from the decomposed video frame to form a filtered video frame.
One advantage of the present invention is the provision of a new method for removing a checkerboard-like noise artifact from a captured composite NTSC video frame without blurring the edges of images within the video frame.
Another advantage of the present invention is the provision of an improved method for removing a checkerboard-like noise artifact from a captured composite NTSC video frame without blurring the edges of images within the video frame.
Yet another advantage of the present invention is the provision of a new apparatus for removing a checkerboard-like noise artifact from a captured composite NTSC video frame without blurring the edges of images within the video frame.
Still another advantage of the present invention is the provision of an improved apparatus for removing a checkerboard-like noise artifact from a captured composite NTSC video frame without blurring the edges of images within the video frame.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiment.